I installed Bitdefender Antivirus as a trial a few days ago. If Autopilot is active, Game Mode is active on my PC in error. I tracked it down to Open Broadcaster Software sitting idle in the background. If I close OBS, the mode is changed to Work or something else, and as soon as I restart OBS, it is changed back to Game Mode.
OBS is a screen recording/streaming application. It is often used to record/stream games, but it has itself nothing to do with gaming. As long as it is only sitting idle in the taskbar, it should not trigger Game Mode.
Website of OBS: https://obsproject.com/forum/
Usually installed in "C:\Program Files\OBS\OBS.exe"
Or the new multiplatform beta: "C:\Program Files\OBS Multiplatform\bin\64bit\obs64.exe"